LONDON (Reuters) - Foreign powers hope threatening Libyan leader Muammar Gaddafi with a war crimes trial at The Hague will help drive him from office, but some worry such talk might instead leave him thinking he has no way out.

The United Nations Security Council voted unanimously to refer Libya to the International Criminal Court following its crackdown on protesters. ICC chief prosecutor Luis Moreno-Ocampo said on Monday attacks on civilians could be a crime against humanity and warranted a full investigation.

But -- just as with previous ICC probes into Congolese warlords, Sudan's president and Uganda's Lord's Resistance Army -- there is the lingering worry that prosecutions will make compromise and finding a solution harder.

Part of the problem, experts say, is that there is simply no real way to know what impact the threat will have on Libya's always somewhat erratic leader.

"It's a difficult balancing act," said Alia Brahimi, a research fellow on North Africa at the London School of Economics. "There is a risk that taking an absolute moral and legalistic approach and talking about war crimes charges simply reinforces Gaddafi's idea that he has nowhere else to go and no option to step down. But on the flip side, it sends a strong message to those around him."

Homegrown amnesty, truth and reconciliation processes -- rather than international prosecutions -- have been key to the resolution of several political crises or conflicts once thought intractable, such as the conflict between South Africa's white apartheid rulers and the black majority.

Many also doubt Northern Ireland's decades of violence could have been brought hopefully to a close if Britain had still been looking to prosecute sometime IRA militants.

A week into Libya's uprising, the country is effectively divided between Gaddafi loyalist and opposition forces in what some fear could be the opening stages of a civil war. Foreign governments say hundreds if not thousands have been killed already, while aid agencies fear a humanitarian crisis.

PROSECUTIONS CARRY RISKS

Outside powers demand that Gaddafi stand down, threatening no-fly zones, sanctions and possibly further military action -- although critics say that can also back intransigent rulers into a corner.

But the foreign powers say the risk of war crimes charges should deter followers from attacking civilians and might help prompt his ouster.

"International prosecutions can sometimes carry risks, such as causing brutal dictators to entrench rather than step down and face justice," said Matthew Waxman, professor at Columbia Law School and fellow at the U.S. Council on Foreign Relations.

"However, (they) can also help isolate perpetrators... hastening their demise while also laying the foundation for longer term stability and serving broader interests in justice and deterrence."

It is possible any war crimes prosecution could still be halted in its tracks if foreign powers chose to do so.

Interviewed by Reuters in 2005 shortly before the ICC issued an arrest warrant for the head of Uganda's LRA leader Joseph Kony, prosecutor Moreno-Ocampo said he might in general agree to halting proceedings in a country if that would bring peace.

Some in Uganda and elsewhere had warned that issuing warrants against the LRA for child abduction and killing might make it impossible to reach an agreement with them.

Kony ultimately refused to sign a peace deal after talks hosted by South Sudan, some say because he feared ICC prosecution. He and his fighters fled into nearby Congo and are still at large, continuing to raid villages there and in Sudan.

But Human Rights Watch's head of the international justice programme, Richard Dicker, said it was now barely even legally possible to simply cancel proceedings.

"The world has changed with the passing of the Rome Statute," he said, referring to the 2002 treaty establishing the ICC. "There's just not the legal option to offer... to stop the legal process. The option of letting Gaddafi walk away without any legal consequences just isn't on the table any more."

UNEVEN PLAYING FIELD

In reality, international justice remains likely to be highly selective. Any one of the permanent five UN Security Council members of the U.S., Britain, France, Russia or China can effectively block a probe.

That means Chinese actions in Tibet and elsewhere, Russian clampdowns in Chechnya or alleged Western abuses in Iraq, Afghanistan and Guantanamo Bay are all off the agenda.

Close friends of Security Council powers such as U.S. ally Israel or China's friends Myanmar or Sri Lanka also tend to enjoy more diplomatic cover.

"It's a far from perfect system... an uneven playing field," said Human Rights Watch's Dicker.

"But I believe... we are moving in the right direction. If you look at eastern Congo, you have warlords who have been given amnesty time and time again... in a short-term search for peace. They have returned to commit even more vicious atrocities. You have to have systems that will bring justice."

Others say that -- like the threat of economic sanctions or military action -- at the end of the day the prosecution threat may simply become another diplomatic bargaining chip.

"A war crimes indictment demonstrates the resolve of the international community," said Thomas Barnett, chief analyst of political risk consultancy Wikistrat. "To the extent that it pushes an embattled leader into a corner, it can likewise be retracted as part of the collective bargaining for an acceptable exit scenario for the leader, his family and top associates."

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